Shaped interlayer for heads-up display windshields and process for preparing same

ABSTRACT

A self-supporting adhesive web  10  having a uniform thickness profile across at least 20% of its width as shown by areas A and B and a wedge-shaped thickness profile in areas C and D. As shown in FIG.  2,  a laminate comprises sheets of glass  12  and  14  having sandwiched therebetween adhesive interlayer  16 . Interlayer  16  has a uniform thickness profile extending from edge  18  to point  20  and a wedge-shaped thickness profile from point  20  to edge  22.

This application is a continuation of U.S. patent application Ser.No.10/478,623, filed Nov. 17, 2003, which is incorporated herein byreference, which is a 371 of PCT/US02/21111, filed Jun. 17, 2002, whichclaims the benefit of U.S. Provisional Patent Application No.60/298,802, filed Jun. 15, 2001.

BACKGROUND OF THE INVENTION

Heads-up instrument displays (HUD) for vehicles have been used toprovide virtual images that appear to be located ahead of the vehiclewindshield toward the front of the vehicle. These displays provide theadvantage of increased safety since the operator does not have to divertattention significantly from viewing the outside to check instruments.

Most conventional windshields are made by placing a layer of adhesive,e.g. polyvinyl butyral (PVB) or polyurethane, which has a substantiallyuniform thickness between two sheets of glass and laminating thesandwiched assembly in an autoclave. In a conventional HUD, where theimage source is located away from the windshield, the light from theimage source reflects off the windshield toward the viewer who sees theimage floating in space beyond the windshield. If a conventionalwindshield is used, the viewer sees two separated images, one from theinside surface of the windshield and one from the outside surface. Whenthese two images do not align in the viewer's sight, a ghost image isseen which interferes with acceptable viewing.

Approaches to reduce the ghost image problem include use of an adhesiveinterlayer disposed within the windshield with the interlayer having apredetermined wedge angle. The wedge angle is selected pursuant to theanticipated installation angle of the windshield, thickness of the glasssheets, and angle of incidence of the projected image so as tosubstantially superimpose the images generated from a dashboard displaydevice that is reflected from the inside surface and outside surface ofthe windshield into a substantially singular image in the eyes of thevehicle operator. Among the approaches are those disclosed in U.S. Pat.No. 5,013,134 and Published PCT Application WO 91/06031 and U.S. Pat.No. 5,639,538.

The wedge angle for HUD projection devices is established by using anadhesive sheet having a wedge-shaped thickness profile extendingcontinuously across the width from edge to edge of the sheet. Such asheet and a process for preparing the sheet are disclosed in U.S. Pat.No. 5,087,502.

Web handling problems are encountered in manufacturing and transportingwebs having a wedge-shaped thickness profile extending continuouslyacross the width of the sheet. Web walking is the term used to describesheeting that moves uncontrollably in the transverse direction as it isconveyed or processed. Telescoping is a term that describes what occurswhen the core or individual layers of a rolled web becomes offset, orunevenly rolled. Web walking and telescoping damage the web and renderit difficult or impossible to use in preparing windshields. Theseproblems also limit tinting of the web. While special web handlingequipment and procedures can be used with varying degrees of success,this is expensive and usually requires duplicating existing equipmentused in preparing conventional adhesive sheeting. Making only shortrolls may alleviate these problems. However, short rolls necessitatefrequent changing of rolls during production and by the customer whoprocesses the sheeting into windshields. In addition, shapes provided byprior art process often require additional trimming of the web, asextruded, resulting in an economic loss due to scrap created bytrimming. Also, some of the prior art process requires a wider extrusionline due to the additional trimming.

It would therefore be advantageous to provide adhesive sheeting suitablefor HUD windshield manufacture that does not require special webhandling equipment and procedures or the creating of scrap that must bedisposed of or recycled. Changing the shape of the web as extrudedpermits production on a more narrow extrusion line thus assuring supplyto the market and increasing the flexibility of existing manufacturingfacilities.

Shapes which minimize overall thickness while maintaining overallfunctional utility provide further economic advantage in materialsavings. Asymmetrical shapes provide capability to produce wider widthson narrow lines. Asymmetrical shapes can also be utilized to producemultiple wedge shapes simultaneously thus providing additional economicadvantage by minimizing the frequency of long transition times tomultiple shapes required for specific applications.

SUMMARY OF THE INVENTION

In one aspect, the present invention is a continuous web (10) ofself-supporting adhesive sheet useful for making a transparent adhesiveinterlayer (16) comprising: (a) an area of uniform thickness profile(AB) across at least 20% of its width starting at the center of the weband continuing in both directions toward the outer edges of the web, and(b) two areas of variable thickness profile increasing in thickness fromthe outer edges of the web to the area of uniform thickness at thecenter of the web, such that by splitting the web in the region ofuniform thickness (AB), two pieces of sheet are obtained each having anarea of at least 20% uniform thickness. The two areas of variablethickness profile may increase at equal or unequal rates depending onthe specific manufacturing and/or end use requirements.

In another aspect, the present invention is a continuous web ofself-supporting adhesive sheet useful for making a transparent adhesiveinterlayer comprising (a) two areas of uniform thickness profile acrossat least 20% of its width extending from the edges of the web toward thecenter such that by splitting the web near its midpoint between theouter edges, two pieces of sheet are obtained each having an area of atleast 20% uniform thickness and (b) an area of variable thicknessprofile increasing in thickness starting from the center of the web andincreasing linearly at equal or different slope values in the directionof both edges to the areas of uniform thickness along the edges of theweb, wherein a vertex is formed at each juncture where an area ofuniform thickness meets an area of variable thickness, and the verticesmaybe curved such that a sharp edge is not detectable by physicalinspection of the curved vertex.

In another aspect, the present invention is a continuous web ofself-supporting adhesive sheet useful for making a transparent adhesiveinterlayer comprising (a) two areas of uniform thickness profile acrossat least 20% of its width extending from the edges of the web toward thecenter such that by splitting the web in the non-uniform thicknessregion, two pieces of sheet are obtained each having an area of at least20% uniform thickness and (b) an area of variable thickness profileincreasing in thickness in a continuous and non-linear manner, startingfrom the center of the web and increasing in the direction of both edgesto the areas of uniform thickness, wherein a vertex is formed at eachjuncture where an area of uniform thickness meets an area of variablethickness, and the vertices can be curved such that a sharp edge is notdetectable by physical inspection of the curved vertex.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile;

FIG. 2 is a schematic partial sectional view of a transparent laminateshowing the sheet thickness profile of one-half of the adhesive web ofFIG. 1 which has been incorporated in the laminate;

FIG. 3 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform thickness, and the middle section of theweb tapers to an area of minimum thickness;

FIG. 4 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform thickness, and the middle section of theweb tapers to an area of minimum thickness, the area of minimumthickness has a rounded or smoothed thickness profile;

FIG. 5 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are tapered areas of decreasing thickness, and the middlesection of the web tapers to an area of minimum thickness, the area ofminimum thickness having a rounded or smoothed thickness profile;

FIG. 6 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform thickness have a rounded or smoothedthickness profile at the transition to the area of decreasing thicknessprofile in the middle section of the web, and the middle section of theweb tapers to an area of minimum thickness having a rounded or smoothedthickness profile;

FIG. 7 a is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform thickness that taper to an area ofuniform minimum thickness in the middle section of the web;

FIG. 7 b is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform minimum thickness that taper to an areaof maximum thickness in middle section of the web; and

FIG. 8 is a schematic sectional view of a full width self-supportingadhesive web showing its thickness profile, wherein the outer portionsof the web are areas of uniform thickness, the web increasing inthickness towards the middle of the web, then decreasing in thicknesstowards the middle section of the web, the middle section having auniform thickness greater than the thickness of the outer areas ofuniform thickness.

FIG. 9 shows the thickness profile of the PVB web described in Example2, which has dimensions and wedge angles further defined in Table 1.

DETAILED DESCRIPTION OF THE INVENTION

The web sheets of the present invention are finished width vinylmaterial having a length suitable for use in windshields, or any lengthup to and including lengths suitable for finished supply rolls. In thepresent invention, “wedge areas” are areas where the thickness of theweb sheet is changing—that is, not constant—or non-uniform. For thepurposes of the present application, wedge areas can also be referred toherein as areas of non-uniform or variable thickness. In any of the websdescribed in the present application, the area of variable thicknessprofile can increase symmetrically or asymmetrically relative to the webcenterline, depending on the specific manufacturing and/or end userequirements. Web thickness profiles as described herein refer to thethickness of a cross-section of the web.

Referring now to the drawings, there is shown in FIG. 1, aself-supporting adhesive web 10 having a uniform thickness profileacross at least 20% of its width as shown by areas A and B and awedge-shaped thickness profile in areas C and D. As shown in FIG. 2, alaminate comprises sheets of glass 12 and 14 having sandwichedtherebetween adhesive interlayer 16. Interlayer 16 has a uniformthickness profile extending from edge 18 to point 20 and a wedge-shapedthickness profile from point 20 to edge 22. The interlayer is made byslitting web 10 of FIG. 1 at or near its center-line in the transversedirection, cutting the slit web into sheets and incorporating the sheetsin a windshield, windscreen, window, viewpoint, or any other transparentlaminate through which a surrounding environment may be viewed which mayinclude the windshield of an automobile or other overland vehicle, orthe windscreen of an aircraft, etc. The web from the wound rolls can bestretched by known processes such as disclosed in U.S. Pat. No.5,087,502. Surprisingly, no special web handling equipment or proceduresare required in winding the web into large rolls, and there is virtuallyno perceptible visual imparity in the windshield along the line wherethe thickness profile transitions from uniform to wedge. The laminatemay be composed of glass, plastic such as polycarbonate or acrylic orother transparent material.

In one embodiment, a “single-cut” wedge can be obtained directly fromproduction lines, wherein the single cut wedge has the same shape as awedge obtained after slitting a wedge of the present invention at ornear its midpoint. A single cut wedge can be obtained without thenecessity of slitting the double wedge by running the web on single cutproduction line.

The adhesive web of this invention is useful as an interlayer inmanufacturing windshields providing a HUD. The interlayer is disposedwithin the windshield with the wedge extending transversely thereof andtapering inwardly from the upper toward the lower regions of a head-updisplay viewing area which includes an image area.

Referring to FIG. 2, the image area will lie in the region of thewindshield between point 20 and edge 22. The geometry of interlayer 16from point 20 to edge 22 is defined as wedge-shaped, that is thedistance between the inner surfaces of glass sheets 12 and 14 decreaseswhen measured at various points from point 20 to edge 22. This wedgeshape is expressed in terms of the wedge angle created by intersectingplanes parallel to the first and second surfaces of interlayer 16. Thewedge angle is very small. Generally wedge angles from 0.1 to 1.0milliradian will be used.

The interlayer wedge angle is selected pursuant to the anticipatedinstallation angle of the windshield, thickness of the transparent sheetmaterial, and angle of incidence of the projected image so as tosubstantially superimpose the reflected images generated from adashboard display device and reflected from the inboard surface and fromthe outboard surface of the outboard sheet into a substantially singularimage in the eyes of the vehicle operator.

The wedge portion can increase in thickness in a linear fashion or in acontinuous but non-linear fashion. By “continuous but non-linear”, it ismeant that while the overall thickness of the wedge portion of theinterlayer will constantly increase without decreasing (continuousincrease) the rate of increase may not be linear, or the increase may belinear and then non-linear, or there may be regions where the increaseis linear and other regions where the increase is non-linear. Regions ofnon-linear increase can include regions where the slope is increasingaccording to the equation of a curved line, or where the slope of theplane varies along the surface of the web, or a combination of patternswhereby the increased thickness cannot be predicted according to theequation of a straight line. In the present application, the abovediscussion applies whether the thickness of the web is said to beincreasing or decreasing, noting that whether the thickness is said to“increase” or “decrease” will depend upon whether the thickness of theweb increases or decreases relative to the thickness of the startingreference point.

The width, thickness of the area of uniform thickness, and the thicknessprofile of the wedge areas can be controlled using known equipment forextruding plastic material. This can be done by either manually orautomatically adjusting the lips of a flat sheet extrusion die. Theareas of uniform thickness can have a thickness from 380 to 2286micrometers with the wedged areas tapering to provide the desired wedgeangle. In the present application, it is to be understood that there canbe normal variation from the die lip set point in an extrusion process,and the resulting normal variation in web thickness does not render theweb thickness “non-uniform”. For example, a sheet of the presentinvention can be set to be extruded to have a uniform thickness of 400micrometers. However, the thickness at any given point in the area ofuniform thickness may vary unintentionally. It is not known with numericspecificity what normal variation might be in a given extrusion process,but unless the intent of the operator is to change the thickness of thesheet during the extrusion process, any variation of the thickness isherein defined as “normal variation”. The wedged area must have a widthsufficient to accommodate the image area, but otherwise, the size of thearea is not critical provided that the area of uniform thickness of theweb is at least 20% of the total area of the web.

The preferred material for the interlayer of this invention isplasticized polyvinyl butyral which may be prepared by methods known tothose skilled in the art, as is described, for example, in U.S. Pat. No.2,720,501, U.S. Pat. No. 2,400,957 and U.S. Pat. No. 2,739,957. Suchplasticized polyvinyl butyral material is available commercially from,for example, E. I. du Pont de Nemours and Company under the trademarkButacite®. Other useful materials include plasticized polyvinylchloride, polyesters and polyurethanes.

The plasticized polyvinyl butyral structures of this invention arepreferably melt-extruded in a manner such as is described in U.S. Pat.No. 2,829,399. Preferably, the extruded film is quenched in a water bathand dimensionally stabilized in a manner such as that described in U.S.Pat. No. 3,068,525, for example. The film can be printed with a gradatedtinted band as described in either U.S. Pat. Nos. 2,957,766 or3,591,406. The film is preferably extruded in widths up to 3.50 meters,slit at or near the center and wound up as two rolls. Each roll is thentinted off-line to effect a gradated band along the longitudinal edgehaving uniform thickness. No web handling problems are encounteredprovided at least 20% of the web area has a uniform thickness profile.

The wedge profiles described by FIGS. 7 a and 7 b can have rounded orsmoothed vertices. Rounding or smoothing of the vertices can bebeneficial for the manufacturing process and also impart functionalbenefits to a windshield.

EXAMPLES Example 1

PVB (polyvinyl butyral) molten polymer is extruded through a slot typeflat sheet extrusion die to make sheeting for use in the Heads UpDisplay (HUD) systems. This slot type flat sheet extrusion die will havetwo die lips that are essentially parallel until the slot width isadjusted to produce sheeting for use in HUD systems. One or both of thelips are adjustable to alter the width between the opposing lips of thedie slot.

The transverse sheeting thickness is adjusted and controlled byadjusting the slot width of the die to develop the desired thicknessprofile at the end of the extrusion line where the sheeting is woundinto rolls. A finished sheeting thickness target is entered into anautomatic transverse direction thickness control system that hasprogramming to adjust the slot width of the flat sheet extrusion die. Byestablishing the desired finished sheeting thickness target for specificHUD sheeting thickness profiles, various thickness profiles are producedto meet individual application requirements and HUD system needs.

Example 2

Using the process described in Example 1 a PVB web was produced with athickness profile as depicted in FIG. 9 with dimensions and wedge anglesfurther defined in Table 1. This web was slit at the inner slit positionand wound to form two separate rolls. The separate rolls were asymmetricabout the inner slit position and distinct with respect to overall, A1and A2 width and average thickness, flat region B1 and B2 width andaverage thickness, wedge region, C1 and C2 width, average thickness andwedge angle. TABLE 1 Avg Thickness Wedge Angle Width (inches/cm)(mils/mm) (miliradians) A1 49.5/126 37.9/963 A2 44.5/113 36.2/919 B1 17/43  41.2/1046 B2  16/41 39.0/991 C1 32.5/83  36.2/919 0.29 C228.5/72  35.8/909 0.24

1. A continuous web of self-supporting polyvinyl butyral adhesive sheetuseful for making a transparent polyvinyl butyral adhesive interlayercomprising: (a) two areas of uniform thickness profile across at least20% of its width extending from the edges of the web toward the centersuch that by splitting the web at or near its midpoint between the outeredges, two pieces of sheet can be obtained each having an area of atleast 20% uniform thickness, and (b) an area of non-uniform thicknessprofile wherein the thickness of the web is continuously increasingstarting at or near the center of the web and increasing in thedirection of both edges to the areas of uniform thickness along theedges of the web, wherein a vertex is formed at each juncture where anarea of uniform thickness meets an area of non-uniform thickness, andwherein the vertices are curved such that a sharp edge is not detectableby physical inspection of the vertex.
 2. The continuous web ofself-supporting adhesive sheet material of claim 1 wherein saidthickness profile has a wedge angle from 0.1 to 1.0 milliradians.
 3. Thecontinuous web of self-supporting adhesive sheet material of claim 1wherein said uniform thickness is from 380 to 2286 micrometers.
 4. Thecontinuous web of self-supporting adhesive sheet material of claim 2wherein said uniform thickness is from 380 to 2286 micrometers.
 5. Thecontinuous web of self-supporting adhesive sheet material of claim 1wherein the thickness of the web continuously increases starting at ornear the center of the web and increasing linearly in the direction ofboth edges to the areas of uniform thickness along the edges of the web.6. The continuous web of self-supporting adhesive sheet material usefulfor making a transparent adhesive interlayer of claim 1 wherein thethickness of the web increases from the center of the web towards theedges at different rates such that an asymmetric web thickness profileis obtained.
 7. The continuous web of self-supporting adhesive sheetmaterial of claim 5 wherein said thickness profile has a wedge anglefrom 0.1 to 1.0 milliradians.
 8. The continuous web of self-supportingadhesive sheet material of claim 5 wherein said uniform thickness isfrom 380 to 2286 micrometers.
 9. The continuous web of self-supportingadhesive sheet material of claim 7 wherein said uniform thickness isfrom 380 to 2286 micrometers.
 10. The continuous web of self-supportingadhesive sheet material of claim 1 wherein the thickness of the webcontinuously increases in a non-linear manner, starting at or near thecenter of the web and increasing in the direction of both edges to theareas of uniform thickness.
 11. The continuous web of self-supportingadhesive sheet material of claim 10 wherein said thickness profile has awedge angle from 0.1 to 1.0 milliradians.
 12. The continuous web ofself-supporting adhesive sheet material of claim 10 wherein said uniformthickness is from 380 to 2286 micrometers.
 13. The continuous web ofself-supporting adhesive sheet material of claim 11 wherein said uniformthickness is from 380 to 2286 micrometers.
 14. A continuous single cutweb of self-supporting adhesive polyvinyl butyral sheet useful formaking a transparent adhesive polyvinyl butyral interlayer comprising(a) an area of uniform thickness profile across at least 20% of itswidth extending from one edge of the web toward the center, and (b) anarea of non-uniform thickness profile increasing in thickness startingfrom the opposite edge of the web and increasing in the direction of thearea of uniform thickness, wherein a vertex is formed at each juncturewhere an area of uniform thickness meets an area of non-uniformthickness, and wherein the vertices are curved such that a sharp edge isnot detectable by physical inspection of the vertex.
 15. The continuousweb of self-supporting adhesive sheet material of claim 14 wherein saidthickness profile has a wedge angle from 0.1 to 1.0 milliradians, andwherein said uniform thickness is from 380 to 2286 micrometers.